ES2389622T3 - Moisture crosslinked polyolefin compositions - Google Patents

Abstract

A moisture crosslinked thermoset article comprising a polymer composition, wherein said composition comprises: (a) less than 50 percent by weight of an ethylene based polyolefin, wherein said ethylene based polyolefin contains hydrolysable silane groups, and is selects from the group consisting of a depolyethylene homopolymer grafted with an organic silane, a polyethylene copolymer grafted with an organic silane, a copolymer of an ethylenic monomer unsaturated with an organic silane, and mixtures thereof; (b) less than 50 percent by weight of a propylene-based polyolefin selected from the group consisting of a polypropylene homopolymer, a copolymer of propylene with another olefin, and mixtures thereof; and (c) a silanol condensation catalyst, wherein a combined amount of said ethylene-based polyolefin and said propylene-based polyolefin is greater than 50% by weight of said composition; and in which the article is crosslinked by moisture by hydrolysis of said silane groups.

Description

Moisture crosslinked polyolefin compositions

Field of the Invention

The present invention relates to polymeric compositions and their uses, and more particularly to moisture crosslinked compositions of polyethylene based polypropylene based polymers, and to coatings and insulating materials containing these compositions.

Background of the invention

Polypropylenes are ideally suited for the preparation of coatings and insulating materials designed for use at higher operating temperatures than other polyolefins can withstand, such as, for example, polyethylene, which shows lower softening and melting temperatures. Polyethylenes have a maximum melting point, determined by differential scanning calorimetry (DSC), of approximately 135 ° C, while polypropylenes can have melting points of up to 175 ° C. As such, polypropylenes can withstand higher operating temperatures without being permanently damaged or deformed.

Other attractive features of polypropylenes are their high rigidity, abrasion resistance, impact resistance, hardness, low cost and relatively low density. Applications for polypropylene-based coatings and insulations include insulation for electrical wires and cables, heat shrinkable corrosion protective sleeves for high temperature transmission pipe joints, heat shrinkable tubes or forms for electrical insulation and mechanical protection, or other applications that need greater hardness and rigidity than those achieved with polyethylene based systems.

To maximize thermal resistance and physical properties, it is necessary to impart some thermosetting characteristic to the material. This is done by crosslinking the polymer to the extent necessary. This makes the material resistant to melting and flow when heated at a temperature close to or higher than the crystalline melting point of the polymer component with the highest melting point of the composition. This feature is necessary for the production of high temperature insulation materials and heat shrink items. In the latter case, the crosslinking imparts controlled contraction characteristics and returns the melt resistant material when heated to the temperature necessary to carry out the contraction.

Several examples of cross-linked polymer compositions containing polypropylene are known in the prior art. U.S. Pat. No. 6,569,915 describes heat shrinkable articles comprising a radiation crosslinked composition predominantly based on polypropylene and also comprising an ethylene-propylene elastomer. U.S. patents No. 6,455,637, 6,465,547 and 6,794,453 refer to articles comprising moisture crosslinked compositions, predominantly based on polypropylene, which also include amounts of silane grafted polyolefin. Compositions predominantly based on polypropylene, described and claimed in these patents, all have high rigidity, hardness and resistance to thermal deformation, making them suitable for use in demanding applications such as protective sleeves for high temperature transmission pipes at which the temperature Operating is typically in the range of 110-130 ° C, or higher.

There are, however, situations in which it is desirable to provide compositions and articles with rigidity, hardness and mechanical integrity similar to those of crosslinked compositions based on polypropylene, but with a moderate capacity at high temperatures, as determined by the mechanical properties that they depend on the performance of the constituent polymers above their softening points. In this aspect, it is known to provide radiation crosslinked polymeric compositions containing polypropylene, which are predominantly based on intermediate density, linear intermediate density or high density polyethylene, and lower amounts of polypropylene homopolymers or copolymers. These types of compositions are described in US Pat. No. 7,456,231. The need remains, however, for moisture crosslinked compositions containing polypropylene, with a moderate capacity at high temperatures.

Summary of the invention

According to the invention, moisture crosslinkable polymeric compositions, and moisture crosslinked articles prepared therefrom are provided. The compositions and articles are predominantly based on combinations of polyethylene and polypropylene, in which the polyethylene and polypropylene components are each present in the compositions and articles in amounts less than 50 weight percent. The inventors have found that the articles according to the invention, after moisture crosslinking, have a stiffness and hardness similar to those of the prior art polypropylene-containing compositions described above, without the need for polypropylene as the predominant ingredient. These properties can be achieved, for example, by maintaining the ratio polypropylene: polyethylene in the composition similar to that contained in prior art compositions predominantly based on polypropylene. This is achieved by reducing the content of both polypropylene and polyethylene below 50 percent by weight of the composition. In addition, the compositions according to the invention offer an improved extrusion processability, in terms of performance and manufacturing control.

The moisture crosslinked articles according to the invention are suitable for use in applications that require a lower degree of thermal resistance than in the typical case of compositions predominantly comprised of polypropylene. More specifically, the moisture crosslinked articles according to the invention are suitable for use at operating temperatures below the softening points of the polyethylene and polypropylene components, typically up to about 110 ° C. Such items include products for heat shrink tubes for mechanical protection, strain relief and splicing insulation, electrical and electronic connections and terminations; and electrical insulation for wires and cables in which hardness and rigidity at high temperature, and long-term thermal stability are important requirements.

The moisture crosslinkable polymer composition comprises (a) less than 50% by weight of an ethylene-based polyolefin selected from the group comprising polyethylene homopolymers and ethylene copolymers with olefins having from 3 to 20 carbon atoms; (b) less than 50 percent by weight of a propylene-based polyolefin selected from the group comprising polypropylene homopolymers and copolymers of propylene with other olefins; and (c) hydrolysable silane groups. The composition is predominantly based on a combined amount of polyethylene based polyolefin and polypropylene based polyolefin.

The invention provides a moisture crosslinked thermoset article. The article comprises a polymer composition, wherein the composition comprises (a) less than 50 percent by weight of an ethylene-based polyolefin, in which the ethylene-based polyolefin contains hydrolyzable silane groups, and is selected from the group that it consists of a homopolymer of polyethylene grafted with an organic silane, a copolymer of polyethylene grafted with an organic silane, a copolymer of an ethylenic monomer unsaturated with an organic silane, and mixtures thereof; (b) less than 50 percent by weight of a propylene-based polyolefin selected from the group consisting of a polypropylene homopolymer, a copolymer of propylene with another olefin, and mixtures thereof; and (c) a silanol condensation catalyst. The combined amount of the ethylene-based polyolefin and the propylene-based polyolefin is greater than 50% by weight of the composition; and the article is crosslinked by moisture by hydrolysis of the silane groups.

In the thermosetting article cross-linked by moisture according to the invention, the article possesses a sufficient degree of cross-linking, so that when the article is heated to a temperature above the crystalline melting point of the propylene-based polyolefin, it is softened but not It becomes liquid.

In moisture crosslinkable polymeric compositions and in moisture crosslinked thermoset articles according to the invention, the combined amount of the ethylene-based polyolefin and the propylene-based polyolefin in the composition is greater than 50% by weight, for example from about 70% to about 95% by weight. The ethylene-based polyolefin may be present in the composition in an amount from about 30% to about 48% by weight, and the propylene-based polyolefin may be present in the composition in an amount from about 35% to about 48% by weight. .

In the moisture crosslinkable polymer compositions and in the moisture crosslinked thermoset articles according to the invention, the ethylene based polyolefin may comprise a polyethylene homopolymer or a polyethylene copolymer selected from the group comprising low density polyethylene (LDPE), polyethylene High density (HDPE), intermediate density polyethylene (MDPE), very low density polyethylene (VLPE) and linear low density polyethylene (LLDPE).

In the moisture crosslinkable polymeric compositions and in the moisture crosslinked thermoset articles according to the invention, the ethylene based polyolefin may comprise an ethylene copolymer with an olefin having 3 to 20 carbon atoms, wherein the olefin which having 3 to 20 carbon atoms is selected from the group consisting of propylene, butene, hexene, octene, ethylidene norbornene, vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, and mixtures thereof, with the copolymer comprising from about 60% to about 95% by weight of ethylene. For example, the ethylene-based polyolefin may comprise an ethylene-propylene elastomer or an ethylene-propylene-diene elastomer.

In the moisture crosslinkable polymer compositions and in the moisture crosslinked thermoset articles according to the invention, the propylene based polyolefin may comprise a propylene and ethylene copolymer comprising at least about 80% by weight of propylene. The propylene-based polyolefin may comprise a modified propylene by reaction with a compound selected from the group consisting of silane, acrylic acid, methacrylic acid, acrylate, methacrylate, glycidyl methacrylate, anhydride, and mixtures thereof.

In moisture crosslinkable polymeric compositions and in moisture crosslinked thermoset articles according to the invention, hydrolysable silane groups can be incorporated into the composition by grafting an organic silane into a polyolefin component, in the presence of a free radical initiator. Therefore, compositions containing a silane grafted polyolefin component further comprise a free radical initiator. The polyolefin component may comprise the ethylene-based polyolefin or a mixture of the ethylene-based polyolefin with at least a portion of the propylene-based polyolefin. Alternatively, hydrolysable silane groups can be incorporated into the composition by copolymerization of an unsaturated ethylenic monomer with an organic silane.

The moisture crosslinkable polymeric compositions and the moisture crosslinked thermoset articles according to the invention may further comprise one or more optional ingredients selected from the group comprising pigmentation agents, mineral fillers, flame retardant additives, antioxidants, UV stabilizers, lubricants and compatibilizers . When a compatibilizer is added, it can be present in the composition in an amount from about 5% to about 10% by weight, and can be selected from the group consisting of: ethylene-propylene-diene elastomers; crystalline-ethylene propylene elastomers; thermoplastic polyolefin elastomers; metallocene polyolefins; copolymers of cyclic olefins; polyoctanomers; ethylene vinyl acetate copolymers; ethylene-vinyl alcohol copolymers; ethylene alkyl acrylate copolymers; polybutenes; hydrogenated polybutadienes; non-hydrogenated polybutadienes; butyl rubber; modified polyolefins with reactive functional groups selected from the group comprising silanes, alcohols, amines, acrylic acids, methacrylic acids, acrylates, methacrylates, glycidyl methacrylates, and anhydrides; polyolefin ionomers; polyolefin nanocomposites; styrene-butadiene block copolymers; styrene-butadiene-styrene block copolymers; block copolymers of styrene ethylene / propylene styrene; block copolymers of styrene-ethylene / butylene-styrene; and their mixtures. For example, the compatibilizer may comprise a styrene-ethylene / butylene-styrene copolymer.

In moisture crosslinkable polymeric compositions and in moisture crosslinked thermoset articles according to the invention, the weight ratio between polypropylene-based polyolefin and polyethylene-based polyolefin can be from about 1.6: 1 to about 0.7 : 1, or from about 1.4: 1 to about 0.9: 1.

Thermosetting articles cross-linked by moisture according to the invention may have a gel fraction greater than about 25%, and may be heat shrinkable. For example, the article may be in the form of a product for heat shrink tubing such as wire or cable insulation.

Detailed description

The invention provides moisture crosslinkable polymeric compositions and moisture crosslinked articles prepared therefrom. The compositions and articles of the invention are predominantly based on combinations of ethylene-based polyolefins and propylene-based polyolefins, each of which is contained in the compositions and articles in amounts less than 50 percent by weight. The use of the term "predominantly" in the present invention, with reference to the compositions and articles according to the invention, means at least 50 percent by weight. Unless stated otherwise, all the percentages mentioned in the present invention are as many percent by weight.

Ethylene-based polyolefins suitable for use in the compositions and articles of the invention include polyethylene homopolymers and copolymers of ethylene with an olefin other than ethylene having from 3 to 20 carbon atoms.

Polyethylene homopolymers and copolymers can be selected from low density polyethylene (LDPE), intermediate density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and very low density polyethylene (VLDPE) . The terms HDPE, LDPE, MPDE, VLDPE and LLDPE, as used in the present invention, are defined in accordance with D 1248 of the American Society for Testing and Materials (ASTM). HDPE and LLPE are preferred in some embodiments of the invention.

Suitable copolymers of ethylene include those in which olefin other than ethylene is selected from the group comprising propylene, butene, hexene, octene, ethylidene norbornene, vinyl acetate, methyl acrylate, ethyl acrylate and butyl acrylate. The ethylene copolymer may also comprise an ethylene propylene or ethylene propylene diene elastomer. Ethylene copolymers are preferably prepared using metallocene catalysts, also known as single-center, stereospecific, or forced geometry catalysts, and may also comprise a bimodal molecular weight distribution. In one embodiment of the invention, the ethylene-based polyolefin comprises a polymerized ethylene-octene copolymer using a so-called metallocene catalyst.

The ethylene-based polyolefin may comprise from about 50 to about 100% by weight of ethylene, for example, from about 60 to about 95% by weight of ethylene, or from about 80 to about 95% by weight of ethylene. The ethylene-based polyolefin can have a density of about 0.85 to 0.97 g / cm 3, a melt flow rate of about 0.1 to 10 dg / min, and a crystalline melting point of at least about 120 ° C .

The ethylene-based polyolefin is present in the composition in an amount that is less than 50 percent by weight, although sufficient to moisture crosslink the article that is formed from the composition. Typically, the amount of the ethylene-based polyolefin is greater than about 5 percent and less than 50 percent by weight, for example from about 5 percent to about 48 percent by weight, from about 10 percent to 48 percent by weight, from about 20 percent to 48 percent by weight, from about 30 percent to 48 percent, or from 34 to 47 percent by weight.

Propylene-based polyolefins suitable for use in the compositions and articles of the invention include polypropylene homopolymers and propylene copolymers with olefins other than propylene. Suitable polypropylene copolymers include copolymers of propylene and ethylene, and modified polypropylene with reactive functional groups, such as silanes, acrylic acids, methacrylic acids, acrylates, methacrylates, glycidyl methacrylates, and anhydrides. When the propylene-based polyolefin is a polypropylene copolymer, it contains at least about 80% by weight of propylene, for example about 90-95% propylene. In one embodiment of the invention, the propylene-based polyolefin is a copolymer comprising about 90-95% propylene and about 5-10% ethylene.

The propylene-based polyolefin can be isotactic in nature, with a density of approximately 0.85 to 0.91 g / cm 3, and a melt flow rate of approximately 0.1 to 10 dg / min. The melting point of the propylene-based polyolefin, determined by DSC, may be at least about 145 ° C, or at least about 150 ° C, it being understood that the maximum melting point of the polypropylene homopolymer is about 165 ° C, and may preferably be at least 20 ° C higher than the operating temperature of the article formed with the composition.

Propylene-based polyolefin is present in the composition in an amount greater than about 5 percent and less than 50 percent by weight, for example from about 5 percent to 48 percent by weight, from about 10 percent to 48 percent. percent by weight, from about 20 percent to 48 percent by weight, from about 35 percent to 48 percent, or from 37 to 47 percent by weight.

As mentioned above, the compositions and articles according to the invention are predominantly based on a combination of polyethylene-based and polypropylene-based polyolefins. Accordingly, polyethylene-based polyethylene and polypropylene-based polyolefins make up more than 50% by weight of the compositions and articles according to the invention. In some embodiments of the invention, polyethylene based on polyethylene and those based on polypropylene comprise from about 65-95%, or from about 70-95%, or from about 75-90%, by weight of the compositions and articles according to the invention. It will be appreciated that the compositions and articles are defined in the present invention including polyethylene based on polyethylene and those based on polypropylene, and all other optional and essential ingredients combined with them. These other ingredients are described later.

The ratio between polyethylene-based polyolefins and polypropylene-based polyolefins can also be varied to vary the properties of articles produced in accordance with the invention. In this aspect, the weight ratio of polyolefin based on polypropylene: polyolefin based on polyethylene is typically within the range of about 5: 1 to 1: 5, more typically about 3: 1 to 1: 3, or about 2: 1 to 1: 2, or about 1.6: 1 to 0.7: 1. When it is desired that the article have properties similar to articles predominantly based on polypropylene, the ratio of polyolefin based on polypropylene: polyolefin based on polyethylene is typically from about 0.9: 1 to 1.5: 1, or from about 0, 9: 1 to about 1.4: 1, or from about 1: 1 to about 1.4: 1.

The compositions and articles of the invention include a silane modified polyolefin component, which comprises either a silane grafted polyolefin or a silane-olefin copolymer. The process for chemically grafting silane molecules into a polymer to form a silane grafted resin, followed by a catalyzed hydrolysis and condensation of the silane, is a well known and established procedure, and is described in US Pat. No. 3,646,155 mentioned above. The preparation of the silane-olefin copolymers is described in US Pat. No. 4,413,066 mentioned above.

The silane groups are introduced into the polyolefin component by reaction of a polyolefin component, or its monomeric precursors, with an organic silane with the general formula RR’SiY2 or RSiY3; wherein R represents a monovalent hydrocarbon radical unsaturated with olefin or hydrocarbonoxy, Y represents a hydrolyzable organic radical and R ’represents a monovalent hydrocarbon radical unsaturated with olefin or hydrocarbonoxy, or a hydrolysable organic radical.

The monovalent hydrocarbon radical unsaturated with olefin or hydrocarbonoxy can be selected from the group comprising vinyl, allyl, butenyl, cyclohexenyl, cyclopentadienyl or cyclohexadienyl radicals.

The hydrolysable organic radical may be selected from the group comprising: alkoxy radicals such as methoxy, ethoxy and butoxy radicals; acyloxy radicals such as formyloxy, acetoxy and propionoxy radicals; maximal radicals such as –ON = C (CH3) 2, -ON = CCH3C2H5 and – ON = C (C6H5) 2; and substituted amino radicals selected from alkylamino and arylamino radicals such as -NHCH3, -NHC2H5 and-NH (C6H5) 2.

In some embodiments, the organic silane has the general formula RSiY3, R is a vinyl radical and Y is a methoxy or ethoxy radical. Examples of organic silanes with this composition are vinyltriethoxysilane and vinyltrimethoxysilane.

The amount of silane that reacts with the polyolefin component depends in part on the reaction conditions and the degree of modification desired in the polyolefin. The proportion may vary from about 0.1 to about 50% by weight, based on the total weight of the silane modified polyolefin component, and can be from about 0.5 to 10% by weight, or from about 1.0 to 2.5% by weight.

When the silane modified polyolefin component is a silane grafted polyolefin, a free radical initiator is mixed with the polyolefin component and the organic silane, to initiate the grafting reaction. The free radical initiator may be an organic peroxide selected from the group comprising benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide and di-tert-butyl peroxide, with dicumyl peroxide being preferred in some embodiments of the invention. The criteria for choosing an appropriate free radical initiator are known to those skilled in the art, and are described in US Pat. No. 3,646,155 mentioned above, and will not be repeated here. The free radical initiator may be added in an amount from about 0.1 to about 1.0% by weight of the silane modified polyolefin component, more preferably from about 0.05 to 0.2% by weight.

The silane grafted polyolefins are formed by reaction of the silane, the polyolefin component and the free radical initiator above the melting point of the polyolefins contained therein, under conditions where the polyolefin component is subjected to mechanical processing, according to the procedures known to those skilled in the art. When the silane-modified polyolefin component comprises a silane grafted polyolefin, the polyolefin component comprises the ethylene-based polyolefin and, optionally, at least a portion of the propylene-based polyolefin.

The silane-olefin copolymers are prepared by polymerization of an unsaturated ethylenic monomer with an unsaturated silane monomer containing one or more hydrolysable groups, preferably an organic silane as described above, such as vinyltrimethoxysilane.

The silane modified polyolefin component is subsequently made in the molten state with a silanol condensation catalyst, to prepare an article shaped according to the invention.

When the silane-modified polyolefin component does not include an amount of the propylene-based polyolefin, or when it is desired to increase the amount of the propylene-based polyolefin in the composition, an amount of the propylene-based polyolefin is also added to the mixture. , to be made in molten state. It will be appreciated, however, that the total amount of the propylene-based polyolefin contained in the composition, and in the shaped article, does not exceed the amounts set forth above, regardless of whether it is included

or not some of the propylene-based polyolefin in the silane grafted polyolefin.

The silanol condensation catalyst may be selected from the group comprising organic bases, carboxylic acids and organometallic compounds that include organic titanates and complexes or carboxylates of lead, cobalt, iron, nickel, zinc and tin. For example, the catalyst may be selected from the group comprising dibutyltin dilaurate, dibutyltin diacetate, dibutyltin octanoate, dioctyltin maleate, dibutyltin oxide and titanium compounds, such as titanium 2-ethylhexoxide. In some embodiments of the invention, the silanol condensation catalyst is dibutyltin dilaurate, although any material that catalyzes the silane condensation reaction can be used. The silanol condensation catalyst may be added in an amount from about 0.01 to about 1 percent by weight of the coating material, for example from about 0.05 to about 0.5 percent by weight, or from about 0, 1 to 0.2 percent by weight.

The composition may further comprise one or more optional ingredients selected from the group comprising pigmentation agents, mineral fillers, flame retardant additives, antioxidants, UV stabilizers, lubricants and compatibilizers.

The optional compatibilizer may be selected from one or more members of the group comprising: any of the ethylene-based polyolefins and propylene-based polyolefins described above; ethylene-propylene-diene elastomers; crystalline-ethylene propylene elastomers; thermoplastic polyolefin elastomers; metallocene polyolefins; copolymers of cyclic olefins; polyoctanomers; copolymers of ethylene with vinyl acetate, vinyl alcohol, and / or alkyl acrylates; polybutenes; hydrogenated and non-hydrogenated polybutadienes; butyl rubber; modified polyolefins with reactive functional groups selected from the group comprising silanes, alcohols, amines, acrylic acids, methacrylic acids, acrylates, methacrylates, glycidyl methacrylates, and anhydrides; polyolefin ionomers; polyolefin nanocomposites; and block copolymers selected from the group comprising styrene-butadiene, styrene-butadiene-styrene, styrene-ethylene / propylene and styrene-ethylene / butylene styrene.

In any given composition according to the invention, the compatibilizer is different from the ethylene-based polyolefin and propylene-based polyolefin components of that particular composition. In addition, when the compatibilizer comprises an ethylene-based polyolefin and / or a propylene-based polyolefin as defined above, the amount of compatibilizer present in the composition is such that the total amounts of the ethylene-based polyolefin and the polyolefin based on Propylene in the composition falls within the ranges described above for these components.

The compatibilizer can be added to the composition in an amount of up to about 25 percent by weight, for example up to about 15 percent, or from about 5 to about 10 percent by weight of the composition. The function of the compatibilizer is primarily to promote the ability to mix ethylene-based polyolefin and propylene-based polyolefin, when mixed together, so that the mixture exhibits a homogeneous behavior during use. The addition of the compatibilizer may not be necessary when the other components of the composition show a natural capacity for mixing or satisfactory performance. The compatibilizer can be added to the composition during the preparation of the silane grafted polyolefin component, that is, by mixing it with the polyolefin component, the organic silane and the free radical initiator. Alternatively, the compatibilizer may be mixed with the silane modified polyolefin component and the silanol condensation catalyst before, or during, melt processing.

The antioxidant stabilizer may be chosen from any suitable antioxidant or mixture of antioxidants, designed to prevent degradation of the composition during melt processing, and subsequent thermal aging of the final product. Examples of suitable antioxidants and thermal stabilizers include the classes of chemicals known as hindered phenols, hindered amines, phosphites, bisphenols, benzimidazoles, phenylenediamines and dihydroquinolines. They can be added in amounts from about 0.1 to 5% by weight of the composition, depending on the aging properties that are needed, and the type and amount of optional destabilizing ingredients in the composition, for example halogenated flame retardants or mineral fillers.

Subjecting the shaped article to moisture, preferably at an elevated temperature, will induce cross-linking of the silane groups by combined hydrolysis and condensation reaction. The atmospheric humidity is usually sufficient to allow crosslinking to occur, but the rate of crosslinking can be increased by the use of an artificially moistened atmosphere, or by immersion in liquid water. For example, crosslinking can be carried out at a temperature above 50 ° C, such as by exposing the article at a temperature of 85 ° C and at a relative humidity of 90% for approximately 100 hours.

The degree of crosslinking is sufficient to provide the crosslinked article with a gel fraction of at least about 25%, for example in the range of about 25-40%. When the article is crosslinked to this degree, subsequent heating of the article at a temperature above the crystalline melting point of the ethylene-based polyolefin or the propylene-based polyolefin, whichever is higher, results in the article being It softens but does not melt, that is, the article does not become liquid. Thus, crosslinking provides the articles according to the invention with thermosetting properties, that is, they are thermosetting.

The following is a description of an illustrative method for preparing a moisture crosslinked article according to the invention, which contains a silane grafted polyolefin component.

The polyolefin component, the silane, a free radical initiator, an optional processing stabilizer and an optional compatibilizer, are premixed and passed through an extruder, at a temperature above the melting point of the polyolefin, and by above the decomposition temperature of the peroxide, to achieve the grafting of the silane in the polyolefin. The polyolefin is completely comprised of an ethylene-based polyolefin or a combination of an ethylene-based polyolefin and a propylene-based polyolefin. The grafted material is then passed through a row for multiple filaments to a cold water container, then cut into granules with a granule filament cutter, and dried.

The grafted polyolefin granules are then mixed with a silane condensation catalyst, an antioxidant stabilizer, and optionally with one or more of the optional ingredients described above. Also, when the grafted material no longer includes a propylene-based polyolefin, or when the grafted material includes an amount of the propylene-based polyolefin, and it is desired to increase the polypropylene content of the composition to a level greater than that of the grafted material An amount of the propylene-based polyolefin can be mixed at this stage with the grafted material. The resulting mixture is then processed in a molten state to form a shaped article.

The melt processing of the composition can be carried out by techniques commonly used in industry, such as extrusion or molding. Examples of extruded articles include sheets, tubes and electrical insulation. In some embodiments, the composition may be co-extruded or laminated with another material of similar or different composition, to form a stratified structure with distinct but intimately bonded layers, each layer having different functional properties. For example, a polymer sheet coated with an adhesive can be prepared by coextrusion or stratification of the composition with an adhesive. In other examples, the composition can be layered with a less expensive or non-crosslinkable layer. Molded articles can be prepared by injection, compression or blow molding, and examples include items for electrical insulation, such as end caps and heat shrink sleeves.

The shaped article is then exposed to moisture, preferably at an elevated temperature, to carry out the crosslinking. The crosslinked article shows the property of softening but not becoming liquid when it is reheated near or above the crystalline melting point of the polyolefin component with the highest melting point, which is typically the propylene-based polyolefin component. Thus, the articles according to the invention show thermosetting properties.

The heat shrinkability can be imparted to the crosslinked articles according to the invention by first heating the article near or above the crystalline melting point of the polyolefin component with the highest melting point, stretching without breaking the softened article beyond the original dimensions of its shape, using relatively low forces, and then fixing the article in its stretched state by rapidly cooling it below the crystalline melting point, using a cooling medium such as air, water or other heat transfer medium. Stretching can be carried out by mechanical, pneumatic or hydraulic means. After cooling, the stretched reticles are maintained in a stable state by the solid crystalline regions of the polyolefin components that have been re-formed, thereby preventing the article from spontaneously recovering its original dimensions. Subsequent overheating of the stretched article above the pressure point of the component with the highest melting point will cause the crystalline regions to melt again, and that the structure elastomerically recovers its original dimensions without stretching. The crosslinked structure provides the initial recovery force and again ensures that the article does not melt and that it maintains its mechanical integrity.

The invention is further illustrated by the following examples. Examples 1 to 3 and Table 1 refer to the preparation of silane grafted resin formulations for incorporation into the compositions according to the invention.

Example 1

A mixture of silane grafted resin was prepared by drumming 50 parts by weight of a propylene-ethylene copolymer, 50 parts by weight of an HDPE homopolymer, 2 parts by weight of a silane, together with an organic peroxide initiator and a processing stabilizer. All components of the mixture are commercially available. The mixture was made in a molten state through a 30: 1 L / D extruder, designed to provide the mixing efficiency needed and the residence time for an effective graft, at a melting temperature above the point of fusion of the polypropylene component. The extruded composition was passed to a cold water container, subsequently cut into granules with a granule filament cutter, and dried.

Example 2

A mixture of silane grafted resin was prepared by drumming 80 parts by weight of an HDPE homopolymer, 20 parts by weight of a styrenic block copolymer as compatibilizer, 2 parts by weight of a silane, together with an organic peroxide initiator and a processing stabilizer. All components of the mixture are commercially available. The mixture was made in the molten state and granulated as described above in Example 1, the melt processing temperature being greater than the melting point of the HDPE homopolymer.

Example 3

A mixture of silane grafted resin was prepared by drumming 100 parts by weight of an HDPE homopolymer and 2 parts by weight of a silane, together with an organic peroxide initiator and a processing stabilizer. All components of the mixture are commercially available. The mixture was made in the molten state and granulated as described above in Example 1, the melt processing temperature being greater than the melting point of the HDPE homopolymer.

Table 1

Example 1

Example 2 Example 3

Polypropylene (A)

fifty 0 0

Polyethylene (B)

fifty 80 100

Compatibilizer (C)

0 twenty 0

Silane (D)

2 2 2

Peroxide (E)

0.084 0.084 0.084

Antioxidant (F)

2.66 2.9 2.9

Vehicle for silane (G)

2,084 2,084 2,084

Total (parts by weight)

106,828 107,068 107,068

(A): 90-95% propylene and 5-10% ethylene copolymer (B): HDPE homopolymer with a density of 0.960 g / cm3 and a melt flow rate of 5.0 dg / min (C ): styrene-ethylene / butylene-styrene linear block copolymer with a polystyrene content of 13% (D): vinyltrimethoxysilane (E): dicumyl peroxide (F): hindered phenol antioxidant (G): porous resin vehicle for the silane

Example 4

This example describes the preparation of an extruded moisture crosslinked sheet according to the invention.

The granules produced in Example 1, predominantly comprised of a grafted mixture with silane of

5 polyethylene and polypropylene were mixed with additional ingredients as described in Table 2 below, in the amounts indicated. In particular, 100 parts by weight of the grafted granules were mixed with a total of 7.5 parts by weight of the compatibilizer, 14 parts by weight of the antioxidant, 1.5 parts by weight of the catalyst and 0.5 parts by weight of pigment black. On a percentage basis, the total polypropylene content in the composition was 37.89 percent by weight, and the total polyethylene content was also 37.89 percent in weight.

10 weight, the other ingredients comprising 24.21 percent by weight of the composition.

The combined ingredients were passed, at a melt temperature of approximately 180 ° C, through a 24: 1 single screw L / D extruder, equipped with a single layer sheet extrusion row. The necessary width and thickness dimensions of the extruded sheet were fixed by passing it through a cluster of 3 cooled calendering rollers, and then rolled into reels.

The sheet was crosslinked by conditioning the rolled sheet in reels at a temperature of 85 ° C and at a relative humidity of 90% for approximately 100 hours. This crosslinked sheet was analyzed to determine the degree of crosslinking and its mechanical properties, as indicated in Table 3.

Example 5

This example describes the preparation of an extruded moisture crosslinked sheet according to the invention.

The granules produced in Example 1, predominantly comprised of a mixture grafted with polyethylene and polypropylene silane, were mixed with additional ingredients as described below in Table 2, in the amounts indicated. In particular, 100 parts by weight of the grafted granules were mixed with 14 parts by weight of the antioxidant, 1.5 parts by weight of the catalyst and 0.5 parts by weight of black pigment. On a percentage basis, the total polypropylene content in the composition was 40.34 percent by weight, and the

The total polyethylene content was also 40.34 percent by weight, the other ingredients comprising 19.31 percent by weight of the composition.

The combined ingredients were formed on an extruded sheet and were crosslinked by moisture as described in Example 4, and the mechanical properties of the crosslinked sheet are presented in Table 3.

Example 6

This example describes the preparation of an extruded moisture crosslinked sheet according to the invention.

The granules produced in Example 2, which predominantly comprise a silane grafted polyethylene homopolymer, were mixed with additional ingredients as described below in Table 2, in the 5 amounts indicated. In particular, 50 parts by weight of the silane grafted granules were mixed with 50 parts by weight of the 90-95% propylene copolymer and 5-10% ethylene used in Example 1, 7.5 parts by weight of the antioxidant , 1.5 parts by weight of the catalyst and 0.5 parts by weight of black pigment. On a percentage basis, the total polypropylene content in the composition was 45.66 percent by weight, and the total polyethylene content was 34.12 percent by weight, the other ingredients comprising 20.22 per weight percent

10 of the composition.

The combined ingredients were formed on an extruded sheet and were crosslinked by moisture as described in Example 4, and the mechanical properties of the crosslinked sheet are presented in Table 3.

Example 7

The granules produced in example 3, predominantly comprising a polyethylene homopolymer

Grafted with silane, they were mixed with additional ingredients as described below in Table 2, in the amounts indicated. In particular, 50 parts by weight of the silane grafted granules were mixed with 50 parts by weight of the 90-95% propylene copolymer and 5-10% ethylene used in Example 1, 7.5 parts by weight of the antioxidant , 1.5 parts by weight of the catalyst and 0.5 parts by weight of black pigment. On a percentage basis, the total polypropylene content in the composition was 45.66 percent by weight, and the content

Total polyethylene was 42.65 percent by weight, the other ingredients comprising 11.69 percent by weight of the composition.

The combined ingredients were formed on an extruded sheet and were crosslinked by moisture as described in Example 4, and the mechanical properties of the crosslinked sheet are presented in Table 3.

Example 8

This example is the same as Example 7, except that the composition was formulated with 55 parts by weight of the silane grafted granules of Example 3 and 45 parts by weight of the propylene-ethylene copolymer of Example 1. On a basis of As a percentage, the total polypropylene content in the composition was 41.09 percent by weight, and the total polyethylene content was 46.91 percent by weight, the other ingredients comprising 12.00 percent by weight of the composition.

30 Table 2

Example 4

Example 5 Example 6 Example 7 Example 8

Grafted Resin (Ex. 1)

100 100 0 0 0

Grafted Resin (Ex. 2)

0 0 fifty 0 0

Grafted Resin (Ex. 3)

0 0 0 fifty 55

Polypropylene (A)

0 0 fifty fifty Four. Five

Compatibilizer (B)

7.5 0 0 0 0

Antioxidant (C)

14 14 7.5 7.5 7.5

Catalyst (D)

1.5 1.5 1.5 1.5 1.5

Black pigment

0.5 0.5 0.5 0.5 0.5

Total

123.5 116 109.5 109.5 109.5

(A): 90-95% propylene and 5-10% ethylene copolymer (B): in example 4, the compatibilizer is a combination of 5.0 parts by weight of a linear block styrene-ethylene block copolymer / butylene-styrene with a polystyrene content of 13%, and 2.5 parts by weight of a thermoplastic (vulcanized) elastomer comprised of polypropylene and partially cross-linked EPDM rubber. (C): hindered phenol antioxidant (D): dibutyltin dilaurate catalyst

Table 3

Property

Example 4 Example 5 Example 6 Example 7 Example 8

Gel fraction (%) (A)

38 39 28 30 3. 4

Hot tensile strength (psi) (B)

37 (0.26 MPa) 45 (0.31 MPa) 37 (0.26 MPa) 42 (0.29 MPa) 40 (0.28 MPa)

Hot elongation (%) (C)

140 70 90 80 90

Tensile strength (psi)

4450 (30.68 MPa) 4520 (31.16 MPa) 5210 (35.92 MPa) 5340 (36.82 MPa) 4930 (33.99 MPa)

Breaking Elongation (%)

450 450 540 530 510

(A): Degree of crosslinking (B): at 200 ° C and elongation of 100% (C): at 200 ° C

Although the invention has been described in relation to certain specific embodiments, it will be appreciated that it is not intended to be limited thereto. More precisely, the invention is intended to cover all embodiments that fall within the scope of the following claims.

Claims (15)

1. A moisture-crosslinked thermoset article comprising a polymer composition, wherein said composition comprises:

(to)

 less than 50 percent by weight of an ethylene-based polyolefin, wherein said ethylene-based polyolefin contains hydrolysable silane groups, and is selected from the group consisting of a polyethylene homopolymer grafted with an organic silane, a polyethylene copolymer grafted with an organic silane, a copolymer of an ethylenic monomer unsaturated with an organic silane, and mixtures thereof;

(b)

 less than 50 percent by weight of a propylene-based polyolefin selected from the group consisting of a polypropylene homopolymer, a copolymer of propylene with another olefin, and mixtures thereof; Y

(C)

a silanol condensation catalyst;

wherein a combined amount of said ethylene-based polyolefin and said propylene-based polyolefin is greater than 50% by weight of said composition; Y wherein the article is crosslinked by moisture by hydrolysis of said silane groups.

2.

The moisture crosslinked article according to claim 1, wherein the article possesses a sufficient degree of crosslinking so that, when the article is heated to a temperature above the crystalline melting point of the propylene based polyolefin, it softens but It does not become liquid.

3.

The moisture crosslinked article according to any preceding claim, wherein said combined amount of said ethylene-based polyolefin and said propylene-based polyolefin in said composition is from 70-95% by weight.

Four.

The moisture crosslinked article according to any preceding claim, wherein said polyethylene homopolymer is selected from the group consisting of low density polyethylene (LDPE), high density polyethylene (HDPE), intermediate density polyethylene (MDPE), polyethylene Very low density (VLDPE), linear low density polyethylene (LLDPE), and mixtures thereof.

5.

The moisture crosslinked article according to any preceding claim, wherein the polyethylene copolymer comprises an ethylene copolymer with an olefin having 3 to 20 carbon atoms;

wherein said olefin having 3 to 20 carbon atoms is selected from the group consisting of propylene, butene, hexene, octene, ethylidene norbornene, vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, and their mixtures; and wherein said polyethylene copolymer comprises from 60% to 95% by weight of ethylene.

6.

The moisture crosslinked article according to claim 5, wherein said ethylene copolymer with an olefin having 3 to 20 carbon atoms is an ethylene-propylene elastomer or an ethylene-propylene-diene elastomer.

7.

The moisture crosslinked article according to any preceding claim, wherein said ethylene-based polyolefin is present in said composition in an amount from 30-48% by weight.

8.

The moisture crosslinked article according to any preceding claim, wherein said propylene-based polyolefin comprises a propylene and ethylene copolymer comprising at least 80% by weight of propylene.

9.

The moisture crosslinked article according to any preceding claim, wherein said propylene-based polyolefin comprises a propylene modified by reaction with a compound selected from the group consisting of silane, acrylic acid, methacrylic acid, acrylate, methacrylate, glycidyl methacrylate, anhydride, and mixtures thereof.

10.

The moisture crosslinked article according to any preceding claim, wherein said propylene based polyolefin is present in said composition in an amount from 35-48% by weight.

eleven.

The moisture crosslinked article according to any preceding claim, further comprising one or more ingredients selected from the group consisting of pigmentation agents, mineral fillers, flame retardant additives, antioxidants, UV stabilizers and lubricants.

12.

The moisture crosslinked article according to any preceding claim, wherein the polymer composition includes a compatibilizer selected from the group consisting of: ethylene propylene diene elastomers; crystalline-ethylene propylene elastomers; thermoplastic polyolefin elastomers; metallocene polyolefins; copolymers of cyclic olefins; polyoctanomers; ethylene vinyl acetate copolymers; ethylene-vinyl alcohol copolymers; ethylene alkyl acrylate copolymers; polybutenes; polybutadienes

hydrogenated; non-hydrogenated polybutadienes; butyl rubber; modified polyolefins with reactive functional groups selected from the group comprising silanes, alcohols, amines, acrylic acids, methacrylic acids, acrylates, methacrylates, glycidyl methacrylates, and anhydrides; polyolefin ionomers; polyolefin nanocomposites; styrene-butadiene block copolymers; styrene-butadiene-styrene block copolymers; 5 block copolymers of styrene-ethylene / propylene-styrene; block copolymers of styrene-ethylene / butylene styrene; and their mixtures; wherein the compatibilizer is present in the composition in an amount from 5-10% by weight; Y wherein the compatibilizer comprises an ethylene-based polyolefin and / or a propylene-based polyolefin as defined in any preceding claim, and the amount of the compatibilizer present in the polymer composition is such that the total amounts of the polyolefin based on ethylene and the propylene-based polyolefin in the composition fall within the amounts defined in any preceding claim.

13.

The moisture crosslinked article according to claim 12, wherein the compatibilizer comprises a styrene-ethylene / butylene-styrene block copolymer.

14.

The moisture crosslinked article according to any preceding claim, wherein the

The weight ratio between the propylene-based polyolefin and the ethylene-based polyolefin is from 1.6: 1 to 0.7: 1, for example from 1.4: 1 to 0.9: 1. 15. The moisture crosslinked article according to any preceding claim, wherein the article is heat shrinkable.